Controlling Packet Transmission

ABSTRACT

A method, program and apparatus for estimating a bandwidth of a channel from a transmitter to a receiver. The method comprises: receiving a packet stream at the receiver from the transmitter; receiving from the transmitter an indication of data transmitted from the transmitter to one or more other recipients than said receiver between packets of said packet stream; and determining at the receiver, using said indication, an estimate of the bandwidth of said channel. The estimate may enable transmission of packets from the transmitter to be controlled.

This application is a continuation-in-part of U.S. application Ser. No.12/455,908, filed on Jun. 9, 2009 and claims priority under 35 U.S.C.§119 or 365 to Great Britain, Application No. 0822620.1, filed Dec. 11,2008. The entire teachings of the above applications are incorporatedherein by reference.

The present invention relates to controlling packet transmission, and inparticular to estimation of bandwidth capacities of receivers andtransmitters in a packet-based communications system. The invention isparticularly but not exclusively related to real-time IP communicationsystems.

A number of methods exist for estimating bandwidth, and can becategorised in the following three groups:

“Max throughput”—a channel is loaded with data until increased one-waydelay, packet round-trip time RTT, and/or loss is observed. Thebandwidth is the maximum load that goes through without problems.

“Relative delay”—packets of different sizes are sent and theirindividual RTTs/delays are measured. Assuming that one-way transmissiontimes equal packet sizes divided by bandwidth, the bandwidth can beestimated from the slope of the observed (packet size, RTT/delay) graph.The packets must be transmitted with a large interval to avoid networkqueuing, which would otherwise obscure the measurements. Typically, RTTsare employed instead of one-way delays because of the unknown clockoffset between transmitter and receiver. In a modified version, twopackets are sent back-to-back meaning that the last one will always bequeued behind the first one, and the bandwidth can be determined fromthe difference in the two packets' RTTs/delays. For a surveillance ofsuch methods, see e.g.http://vbn.aau.dk/fbspretrieve/6189553/Available_Bandwidth_Estimation.pdf.

Both of the above methods rely on RTT. When a packet k is transmitted,the transmitter notes the time of transmission, Tx(k). When a receiverreceives the packet, it feeds back another packet to the transmittercontaining an identifier for k. The transmitter then finds theRTT=Tfb(k)−Tx(k), where Tfb(k) is the time of arrival of the feedback.

“Blackbox methods”—from a database of generic observable parameters andknown bandwidths, a statistical model is built to describe bandwidths asa function of the observables. For example, the model can be a neuralnetwork. By feeding the trained model with a set of observables for anetwork with unknown bandwidth, it can then return an estimate of thebandwidth.

A different but related problem is that of network rate control forwhich a widespread method is the “Additive increase, multiplicativedecrease” mechanism by Jacobson [V Jacobson, “Congestion avoidance andControl”, 1988]. Typically, such methods are not based on capacityestimation as such, but instead seek to reach an equilibrium ortrade-off between different performance parameters such as loss,roundtrip time, and transmission rate. Such approaches typically lead tovarying transmission rates and occasional loss and jitter, making themof limited use for strict real-time applications.

“Max through-put” and “Relative delay” methods both suffer from theproblem that they require modification of the network load to estimatethe bandwidth. Moreover, “Max through-put” in effect requires anoverload of the channel, obstructing other simultaneous traffic.

RTT-based methods suffer from the additional problem that the feedbackmay be delayed itself, severely impacting the estimation.

“Blackbox methods” are appealing in that they do not suffer from theabove-mentioned problems; unfortunately, the generic input does not ingeneral provide sufficient information for precise bandwidth estimation,making the method inadequate for most applications, including ratecontrol.

It is an aim of the present invention to mitigate the problems discussedabove.

According to one aspect of the present invention, there may be provideda method of estimating a bandwidth of a channel from a transmitter to areceiver, the method comprising: receiving a packet stream at thereceiver from the transmitter; receiving from the transmitter anindication of data transmitted from the transmitter to one or more otherrecipients than said receiver between packets of said packet stream; anddetermining at the receiver, using said indication, an estimate of thebandwidth of said channel.

In embodiments, the estimation may comprise: transmitting packets from aqueue, each packet having a packet size based on data in the packet;determining a transmission time for each packet, based on a transmissionclock; determining a reception time of each packet, based on a receptionclock; supplying to an estimation function successive sets ofobservations including in each set an indication of cross-traffic, atransmission time, reception time and packet size, wherein said estimatefunction may be arranged to provide an estimate of bandwidth for thechannel using the relationship between the bandwidth, the amount of datain the queue, packet size, cross-traffic and the delay betweentransmitting successive packets from the queue.

In alternative embodiments, the estimation may be based on a relativedelay method. For example, the estimation of said bandwidth may begenerated by:

bandwidth estimate=(S(k)+CT(k))/dTr(x)

where dTr(k) is a difference between the reception times of packets kand k−1 of said packet stream at the receiver, S(k) is the size ofpacket k, and said indication comprises an indication of cross-trafficCT transmitted between the transmission time of packet k−1 and packet k.

According to another aspect of the present invention, there may beprovided a program product embodied on a computer-readable medium andcomprising code configured so as when executed at a receiver to: receivea packet stream from a transmitter via a channel; receive from thetransmitter an indication of data transmitted from the transmitter toone or more other recipients than said receiver between packets of saidpacket stream; and determine an estimate of the bandwidth of saidchannel using said indication.

According to another aspect of the present invention, there may beprovided a receiver arranged to receive a packet stream from thetransmitter via a channel, the receiver comprising: an estimatorfunction arranged to receive, from the transmitter, an indication ofdata transmitted from the transmitter to one or more other recipientsthan said receiver between packets of said packet stream; wherein theestimation function is configured to determine an estimate of thebandwidth of said channel using said indication.

According to another aspect of the present invention, there may beprovided a method of controlling transmission of packets from atransmitter to a receiver via a channel, the method comprising:transmitting a packet stream from the transmitter to the receiver;transmitting data from the transmitter to one or more other recipientsthan said receiver between packets of said packet stream; transmittingfrom the transmitter to the receiver an indication of said datatransmitted to the one or more other recipients; receiving back anestimate of a bandwidth of said channel generated by the receiver usingsaid indication; and using the estimated bandwidth to controltransmission of packets from the transmitter.

According to another aspect of the present invention, there may beprovided a computer program product for controlling transmission ofpackets from a transmitter to a receiver via a channel, the programproduct comprising code embodied on a computer-readable medium andconfigured so as when executed at a transmitter to: transmit a packetstream to the receiver; transmit data to one or more other recipientsthan said receiver between packets of said packet stream: transmit tothe receiver an indication of said data transmitted to the one or moreother recipients; receive back an estimate of a bandwidth of saidchannel generated by the receiver using said indication; and use theestimated bandwidth to control transmission of packets from thetransmitter.

According to another aspect of the present invention, there may beprovided a transmitter for controlling transmission of packets from thetransmitter to a receiver via a channel, the transmitter beingconfigured to: transmit a packet stream to the receiver; transmit datato one or more other recipients than said receiver between packets ofsaid packet stream; transmit to the receiver an indication of said datatransmitted to the one or more other recipients; receive back anestimate of a bandwidth of said channel generated by the receiver usingsaid indication; and use the estimated bandwidth to control transmissionof packets from the transmitter.

According to another aspect of the present invention, there may beprovided a method for use in controlling transmission of packets from atransmitter to a receiver via a channel, the method comprising:receiving a packet stream at the receiver from the transmitter; at anestimation function of the receiver, receiving from the transmitter anobservation of cross-traffic, the cross-traffic being an amount of datatransmitted from the transmitter to one or more other recipients thansaid receiver between packets of said packet stream; and in theestimation function at the receiver, using the observation of thecross-traffic to generate an estimate of a bandwidth of said channel;such that transmission of packets from the transmitter is controlledusing the estimated bandwidth.

According to another aspect of the present invention, there may beprovided a computer program product comprising code embodied on acomputer-readable medium and configured so as when executed at areceiver to: receiving a packet stream from a transmitter via a channel;receive from the transmitter an observation of cross-traffic, thecross-traffic being an amount of data transmitted from the transmitterto one or more other recipients than said receiver between packets ofsaid packet stream; and use the observation of the cross-traffic togenerate an estimate of a bandwidth of said channel; such thattransmission of packets from the transmitter is controlled using theestimated bandwidth.

According to another aspect of the present invention, there is provideda receiver arranged to receive a packet stream from a transmitter via achannel, the receiver comprising: an estimator function arranged toreceive from the transmitter an observation of cross-traffic, thecross-traffic being an amount of data transmitted from the transmitterto one or more other recipients than said receiver between packets ofsaid packet stream; and wherein the estimator function is configured touse the observation of the cross-traffic to generate an estimate of abandwidth of said channel, such that transmission of packets from thetransmitter is controlled using the estimated bandwidth.

Another aspect of the invention provides a method of controllingtransmission of packets from a transmitter to a receiver via a channel,the method comprising: transmitting packets from a queue, each packethaving a packet size based on data in the packet; determining atransmission time for each packet, based on a transmission clock;determining a reception time of each packet, based on a reception clock;supplying to an estimation function successive sets of observationsincluding in each set transmission time, reception time and packet size,said estimate function arranged to provide an estimate of bandwidth forthe channel using the relationship between the bandwidth, the amount ofdata in the queue, packet size and the delay between transmittingsuccessive packets from the queue; and using the estimated bandwidth tocontrol transmission of packets.

In the particularly preferred embodiment, the relationship used by theestimation function is:

N(k,i)=max(N(k−1,i)+CT(k,i)−(Tx(k,i)−Tx(k−1,i))*BW(i),0)+S(k,i)

where N(k,i) is the amount of data in the channel packet queue at timeTx(k,i), BW is the bandwidth, S(k,i) is the packet size and CT(k,i)denotes any cross-traffic from the transmitter.

Another aspect of the invention provides a transmitter for transmittingpackets to a receiver via a channel, the transmitter comprising: meansassociated with a queue of packets ready for transmission, each packethaving a packet size based on data in the packet; a transmission clockfor recording transmission time for each packet; means for receiving areception time for each packet, based on a reception clock located atthe receiver; and an estimation function arranged to receive successivesets of observations including in each set transmission time, receptiontime and packet size, said estimation function arranged to provide anestimate of the bandwidth of the channel using the relationship betweenthe bandwidth, the amount of data in the queue, packet size and thedelay between transmitting successive packets from the queue. The meansassociated with a queue at the transmitter can be a store of a queue atthe transmitter or means for despatching packets from a network queue.

Another aspect of the invention provides a receiver arranged to receivepackets transmitted from a transmitter via a channel, the receivercomprising: means for determining a transmission time for each packetbased on information received with the packets; a reception clock fordetermining a reception time for each packet; and an estimation functionarranged to receive successive sets of observations including in eachset transmission time, reception time and packet size, said estimationfunction arranged to provide an estimate of the bandwidth for thechannel using the relationship between the bandwidth, the amount of datain a queue of packets, packet size and the delay between transmittingsuccessive packets from the queue.

A particularly noteworthy feature of the described embodiments of thepresent invention is the fact that the bandwidth estimation is based onobservation of one way transmission delays. Thus, it is not subject tothe difficulties associated with RTT-based methods. By using thetechniques described herein, it can effectively be determined ifcongestion problems are in one or another direction.

The invention is applicable for one-to-one and multicasting scenarios.In multicasting scenarios, the method can effectively estimate separateand possibly different up and downlink capacities of each node in anetwork.

Moreover, because a queuing model is employed, the methods discussedherein provide an estimate of bandwidth from whatever traffic isactually sent, and can thus work directly on ongoing traffic due to, forexample, real-time applications.

The estimated bandwidth can be used to control transmission of packetsin a number of different ways. Real-time rate control can beimplemented, or overlay network topology selection can be based on theestimated bandwidth. As compared to the dedicated rate control mechanismdiscussed above for example in Jacobson, the methods described hereinprovide an actual bandwidth estimate making it useful in a wider rangeof applications.

For a better understanding of the present invention and to show how thesame may be carried into effect, reference will now be made by way ofexample to the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating flow of packets between atransmitter and a receiver;

FIG. 2 is a timing diagram;

FIG. 3 is a highly schematised diagram illustrating cross-trafficbetween a transmitter and multiple receivers;

FIG. 4 is a schematic block diagram of circuitry at a receiver toimplement one embodiment of the invention; and

FIG. 5 is a schematic block diagram of a multicast scenario.

FIG. 1 is a highly schematised diagram illustrating the flow of packetsbetween a transmitter 2 and a particular receiver 4, the receiver beingdenoted i. In the packet stream, the sequence numbers of the packets aredenoted using k. FIG. 1 illustrates a packet (k,i) about to betransmitted, and the two preceding packets already having beentransmitted. The packets are conveyed from the transmitter to thereceiver over a channel with a certain bandwidth. The transmitter I hasa clock 6 which is used to provide timing information associated withtransmitted packets. This can be in the form of timestamps within eachpacket, or can be provided as additional side information, preferablypiggybacked to the packet in question. This is shown schematically inFIG. 1 where the side information is denoted t(k,i) for the sequencenumber k of the appropriate packet. The transmission time of a packetwith sequence number k in a stream going to recipient i is denoted byTx(k,i) and is the clock reading. Where timestamps are not provided,side information t(k,i) is encoded and quantised as described below.

FIG. 2 is a timing diagram illustrating how in one particular embodimentthe transmission time Tx(k,i) can be recursively recovered at thereceiver side it can be seen from FIG. 2 that transmission time Tx(k,i)is a delay Δ₂ after the transmission time of the preceding packetTx(k−1,i). Generally, the delay between packets is near constant, thatis Δ₂ is more or less equal to Δ₁, the delay between the earlier twopreceding packets. Thus, an estimate for Δ₂ can be obtained by thefollowing:

α(Tx(k−1,i)−Tx(k−2,i))

where α is less than or equal to 1. Then,

Tx(k,i)=Tx(k−1,i)+Δ₂ +t(k,i).

The t(k,i) is calculated, quantised and transmitted, allowing Tx(k,i) tobe recursively recovered from the following equation:

Tx(k,i)=Tx(k−1,i)+α(Tx(k−1,i)−Tx(k−2,i))+t(k,i).

For use in multicast scenarios, the amount of cross traffic must beencoded, quantised and transmitted along with the outgoing packetstream. FIG. 3 illustrates the concept of cross traffic which is theamount of traffic sent to other recipients than the recipient of oneparticular packet stream. FIG. 3 illustrates three recipients, receiveri, receiver j, receiver h, i and j of which are receiving packets fromtransmitter 2.

One particular definition of cross-traffic for packet k of recipient iis:

CT(k,i)=sum_(mj)(S(m,j)), with m≠k and Tx(k−1,i)<Tx(m,j)Fx(k,i)  Equation (1)

where S(m,j) is the size of packet m going to recipient j. This is theamount of data sent to other recipients in between packets k−1 and k forrecipient i. The CT(k,i) cross-traffic can be encoded in various ways,for example relative to S(k,i) or relative to an estimate of the totalchannel capacity.

In order to describe a technique for estimating the bandwidth betweentwo nodes in a 1 to 1 connection (that is, the transmitter 2 andreceiver 4, reference will now be made to FIG. 4 which incorporates anestimation function at the receiver side.

FIG. 4 illustrates a schematic block diagram of functional blocks at thereceiver 4. A decoder 8 receives a packet and decodes the encoded sideinformation about transmission time to obtain an estimate of thetransmission time of the packet Tx(k,i). Also, a local clock 10 providesa reading denoting the arrival time of the packet, Rx(k,i). From thesetwo quantities, it is possible to compute the raw packet delay:

D(k,i)=Rx(k,i)−Tx(k,i)

A separate calculation function 12 can be provided for this in certainembodiments for clock offset. It will be appreciated that it iseffectively taken into account in any event in the following analysis.

Of course, D(k,i) is not an accurate measurement of the actualtransmission delay, because Rx(k,i) and Tx(k,i) are measured withrespect to different, non-synchronised clocks. D(k,i) can be describedby:

D(k,i)=Dx(k,i)+c(k,i)

where Dx(k,i) is the true delay and c(k,i) is the measurement error dueto clocks not being synchronised. The assumption is made herein thatalthough c(k,i) is unknown, it is close to constant over time.

The receiver 4 includes an estimation function 14 which receives aseries of observations for each of Tx(k,i), Rx(k,i), CT(k,i) and S(k,i).It will be appreciated that CT(k,i) is encoded, quantised andtransmitted with the packet stream. S(k,i) is readily available in anypacket based system: it is the total packet sizes (e.g. in bytes) whichis required for meaningful reception of data typically, it is in the IPheader. These observations are used to provide estimates for thebandwidth of the channel on the uplink BW_(UP)(i), the amount of dataN(k,i) in the channel packet queue at time Tx(k,i), and the measurementerror due to clocks not being synchronised, c(k,i). The estimation isbased on the following theory.

Assume that the total outgoing packet stream of the transmitter islimited by a channel with bandwidth BW_(UP)(i), and that this channelemploys packet queuing when overloaded. Thus we write:

Dx(k,i)=N(k,i)/BW _(UP)(i)+e(k,i)

or equivalently,

D(k,i)=N(k,i)/BW _(UP)(i)+c(k,i)+e(k,i)  Equation (2)

Here, N(k,i) is the amount of data in the channel packet queue at timeTx(k,i), i.e., immediately after packet (k,i) is loaded on the channel.That is, the true transmission delay of a packet is determined by theamount of traffic that must be transmitted, divided by the channeltransmission speed, e(k,i) is measurement noise, due to quantizationnoise in Tx(k,i) and channel disturbances.

In turn we can write:

N(k,i)=max(N(k−1,i)+CT(k,i)−(Tx(k,i)−Tx(k−1,i))*BW_(UP)(i),0)+S(k,i)  Equation (3)

where we assume a steady loading of the cross traffic CT(k,i) over thetime interval [Tx(k−1,i), Tx(k,i)]. Equation (3) says that prior toloading packet (i,k), the amount of traffic in the channel packet queueequals:

-   -   what was there last time we put a packet    -   minus what the channel was able to process since then    -   plus any cross traffic added in the same interval        and that the amount of traffic can never become negative.

The estimator uses equations (2) and (3) for estimating BW_(UP)(i),N(k,i) and c(k,i) using the series of observations which are supplied tothe estimator by Tx(k,i), Rx(k,i), CT(k,i) and S(k,i).

One implementation for the estimator 14 is to see the equations as thebasis for a Kalman filter, and solve them as an extended, unscented orparticle Kalman filter. The preferred implementation applies anunscented Kalman filtering. One advantage of Kalman filtering is that itreadily provides error covariance matrices R(i) for the estimates ofBW_(UP)(i), N(k,i), as well as t-test statistics T(i) for the validityof the model from which equations (2) and (3) are derived. This extrainformation provides insight about the confidence of the resultingestimates, providing estimate confidences ψ.

A Kalman filter allows the equations to be solved in a recursive fashionfor each set of observations. It would be possible to use other methodsof recursive calculation. Alternatively, it would be possible to storevalues for the observations over a period of time and use successivesets to solve the equation by numerical analysis.

In a multicast scenario as illustrated diagrammatically in FIG. 3, andmore particularly in FIG. 5, all or some of the plurality of receiversmay execute the algorithm in an estimator.

FIG. 5 illustrates schematically a plurality of receivers, receiver 1 .. . receiver i . . . receiver M. Each receiver receives packets from thetransmitter 2. At least some of the receivers execute the algorithmdescribed in equation 3 in an estimator as described above whichgenerates estimates for the uplink bandwidth at each receiver, togetherwith estimated confidences cp. As mentioned above, the estimatedconfidences can be based on the co-variances R(i) and t-test statisticsT(i) generated by the Kalman filter.

In that case, the transmitter 2 can execute a weighted averagingfunction 16 which averages received multiple estimates BW_(UP)(1),BW_(UP)(i), BW_(UP)(M), etc, weighted using the estimated confidencesφ(1), φ(i), φ(M) respectively to generate one estimate for the uplinkbandwidth. By feeding back the estimate confidences to the transmitter4, the individual estimates can be combined into one according to:

BW _(UP)=sum_(i)(BW _(UP)(i)*f(ψ(i)))/sum_(i)(f(ψ(i)),

where f denotes a function of ψ.

It is possible to improve operation of the estimator by eliminating theclock error c(k,i) from equation 2 Reverting to FIG. 4, the calculationfunction 12 is illustrated which receives values for Tx(k,i) and Rx(k,i)and calculates the perceived delay D(k,i) for each set of observations.A minimum tracking function 13 observes the one way delays D(k,i) togenerate an estimated compensation for the clock c(k,i). In oneembodiment, the minimum tracking function 13 is implemented as a Kalmanfilter which models c(k,i) as a first order model to grasp any clockdrift. Minimum tracking is obtained by employing higher observationnoise in the Kalman filter for higher values of D(k,i). The estimatedclock offset c is supplied to the estimator 14 which can then internallysubtract the clock offset c(k,i) from D(k,i). This allows the clockoffset to be removed from the Kalman filter state, effectivelydecoupling errors in c(k,i) from estimates of BW(k,i) and N(k,i), whichmay accumulate due to imperfections in the handling of the non-linearityof equation 3. Moreover, reducing the state reduces computationalcomplexity of the Kalman filter.

In an improved version, the delays D(k,i) are first compensated forexpected network delay, so that the minimum ofD(i,k)−[N(k,i)]^(e)/[BW_(UP)(i)]^(e), where [N(k,i)]^(e) and[BW_(UP)(i)]^(e) denote current estimates of N(k,i) and BW_(UP)(i)respectively, is tracked.

It will readily be appreciated that in a one-to-one communication case,there is no cross traffic and so CT(k,i) is constantly 0 and there is noneed to supply it to the estimator.

The estimated bandwidth BW_(UP) is transmitted from the receiver 4 tothe transmitter 2 and can then be used by the transmitter to manageuplink bandwidth resources.

For estimation of the downlink bandwidth (bandwidth of the channel atthe receiver), a similar estimator can be applied but the calculation ofthe cross traffic term CT is different. In this case, it is not decodedfrom an encoded amount sent with the packet stream, but is determined bypicking one reference transmitter and calculating the cross traffic asthe amount of data received from other transmitters in between packetsk,i and k from the reference transmitter. Referring to FIG. 3, as anexample, the receiver labelled i could receive packets not only from theillustrated transmitter 2 but from other (non-illustrated) transmitters.

In an alternative embodiment of the invention the bandwidth estimator isimplemented in the transmitter. In this case the information (Rx)relating to the reception of the data packets is transmitted from thereceiver to the transmitter, to be utilised in estimation at thetransmitter.

It will be appreciated that the above embodiments have been describedonly by way of example, and implementations of the present invention maybe apparent to a person skilled in the art given the disclosure herein.

As discussed above, in the case where a node transmits data to more thanone receiving node, in order for a receiving node to determine theuplink bandwidth of the transmitting node it is desirable for thereceiving node to be notified about the amount of data transmitted toother nodes. As will be apparent from the discussion above, providingthis information such that receiving node can estimate the uplinkbandwidth is advantageous in itself. It is not necessary for this to beimplemented using the specific example estimation method describedabove. For example, it could alternatively be implemented in conjunctionwith a known bandwidth estimation method. E.g. a relative delay typemethod would conventionally take the following form. First note that:

dTx(k)=Tx(k)−^(Tx)(k−1)

where Tx(k) is the transmission time of packet k from the transmitter,and dTx(k) is the difference in transmission time between the packet kand a preceding packet k−1. Then assume that:

S(k)/dTx(k)>the true bandwidth,

where S(k) is the size of packet k. The true bandwidth is the unknownactual uplink channel bandwidth and BWE is the bandwidth estimate,Packets k and k−1 may or may not be of different sizes, but S(k) is thesize of packet k.

An estimate BWE of the bandwidth can then be found by:

BWE=S(k)/dTr(k)

where Tr(k) is the reception time of packet k at the receiver, anddTr(k) is the difference in reception time between the packet k and apreceding packet k−1. If calculations are carried out at the receiver,the transmitter may supply the transmission times as side info.

The equation dTx(k)=Tx(k)−Tx(k−1) above is to help verify the assumptionS(k)/dTx(k)>true bandwidth: if dTx(k) is “large” it is not likely to befulfilled. In embodiments, the receiver may use this calculation todetermine that the bandwidth estimation BWE should not be updatedaccording to BWE=S(k)/dTr(k) if dTx(k) is above a certain threshold.

Under certain assumptions about the channel, it is known thatdTr(k)>dTx(k), so in principle, one can do without calculating dTx(k).

Using the cross traffic (CT) concept according to one aspect of thepresent invention, the above relative delay method could be improved forexample as follows.

Assume (S(k)+CT(k))/dTx(k)>the true BW;

then BWE=(S(k)+CT(k))/dTr(x);

where CT is the cross traffic transmitted between Tx(k−1) and Tx(k).

The present invention is not limited by the described embodiments, butonly by the appendant claims.

1. A method of estimating a bandwidth of a channel from a transmitter toa receiver, the method comprising: receiving a packet stream at thereceiver from the transmitter; receiving from the transmitter anindication of data transmitted from the transmitter to one or more otherrecipients than said receiver between packets of said packet stream; anddetermining at the receiver, using said indication, an estimate of thebandwidth of said channel.
 2. The method of claim 1, wherein the methodenables transmission of packets from the transmitter to the receiver tobe controlled using the estimated bandwidth.
 3. The method of claim 2,comprising feeding back the bandwidth estimate from the receiver to thetransmitter for the transmitter to use to control transmission ofpackets from the transmitter.
 4. The method of claim 1, wherein theindication is of data transmitted to multiple other recipients.
 5. Themethod of claim 1, comprising receiving at the receiver a series ofobservations for each of: a transmission time Tx(k,i) of a packet k ofsaid stream to the receiver i, a reception time Rx(k,i) of the packet kat the receiver i, the cross-traffic CT(k,i) between the packet k and apreceding packet k−1 of said stream transmitted to the receiver i, and asize S(k,i) of the packet k transmitted to the receiver i; andgenerating said estimate of bandwidth using the series of observations.6. The method of claim 1, comprising generating an estimated confidencefor the estimate of uplink bandwidth.
 7. The method of claim 6, whereinthe estimated confidence is generated based on a co-variance and t-teststatistics generated by a Kalman filter.
 8. The method of claim 6,comprising feeding back estimated bandwidths and respective confidencesto the transmitter from a plurality of receivers, for the transmitter toexecute a weighted averaging function which averages the receivedestimates, weighted using the respective estimated confidences togenerate one combined estimate for the bandwidth, and to use thecombined estimate to manage uplink bandwidth resources.
 9. The method ofclaim 1, wherein said indication is received encoded relative to a sizeof a packet of said stream, and method comprises decoding the indicationat the receiver.
 10. The method of claim 1, wherein said indication isreceived encoded relative to an estimate of a total capacity of saidchannel, and method comprises decoding the indication at the receiver.11. The method of claim 1, wherein said indication comprises anindication of cross-traffic for packet k of said stream, thecross-traffic for packet k being an amount of data sent to the one ormore other recipients in between packets k−1 and k of said stream. 12.The method of claim 11, wherein the cross-traffic is defined by:CT(k,i)=sum_(mj)(S(m,j)), with m≠1(and Tx(k−1,i)<Tx(m,j)<Tx(k,i) whereS(m,j) is the size of a packet m transmitted to one of said otherrecipients j, and Tx(k, i) is the transmission time of a packet k ofsaid packet stream transmitted to said receiver i.
 13. The method ofclaim 1, wherein the estimation comprises: transmitting packets from aqueue, each packet having a packet size based on data in the packet;determining a transmission time for each packet, based on a transmissionclock; determining a reception time of each packet, based on a receptionclock; supplying to an estimation function successive sets ofobservations including in each set an indication of cross-traffic,transmission time, reception time and packet size; said estimatefunction arranged to provide an estimate of bandwidth for the channelusing the relationship between the bandwidth, the amount of data in thequeue, packet size, cross-traffic and the delay between transmittingsuccessive packets from the queue.
 14. The method of claim 13, whereinthe relationship used by the estimation function is:N(k,i)=max(N(k−1,i)+CT(k,i)−(Tx(k,i)−Tx(k−1,i))*BW _(UP)(i),0)+S(k,i)where N(k,i) is the amount of data in the channel packet queue at timeTx(k,i), BW_(UP) is the uplink bandwidth, S(k,i) is the packet size andCT(k,i) denotes the cross-traffic from the transmitter.
 15. The methodof claim 13, wherein the transmission time for each packet is conveyedwith the packet as a timestamp.
 16. The method of claim 13, wherein thetransmission time for each packet is recovered at the receiver based ontime-related side information transmitted with each packet.
 17. Themethod of claim 13, wherein the estimation function operates on the setsof observations in a recursive fashion.
 18. The method of claim 13,wherein the estimation function is a Kalman filter.
 19. The method ofclaim 13, comprising the step of estimating a clock error between thetransmission clock and the reception clock, and filtering the clockerror to simplify operation of the estimation function.
 20. The methodof claim 1, wherein the estimation of said bandwidth is based on arelative delay method.
 21. The method according to claim 20, wherein theestimation of said bandwidth is generated by:bandwidth estimate=(S(k)+CT(k))/dTr(x) where dTr(k) is a differencebetween the reception times of packets k and k−1 of said packet streamat the receiver, S(k) is the size of packet k, and said indicationcomprises an indication of cross-traffic CT transmitted between thetransmission time of packet k−1 and packet k.
 22. A program productembodied on a computer-readable medium and comprising code configured soas when executed at a receiver to: receive a packet stream from atransmitter via a channel; receive from the transmitter an indication ofdata transmitted from the transmitter to one or more other recipientsthan said receiver between packets of said packet stream; and determinean estimate of the bandwidth of said channel using said indication. 23.A receiver arranged to receive a packet stream from the transmitter viaa channel, the receiver comprising: an estimator function arranged toreceive, from the transmitter, an indication of data transmitted fromthe transmitter to one or more other recipients than said receiverbetween packets of said packet stream; wherein the estimation functionis configured to determine an estimate of the bandwidth of said channelusing said indication.
 24. A method of controlling transmission ofpackets from a transmitter to a receiver via a channel, the methodcomprising: transmitting a packet stream from the transmitter to thereceiver; transmitting data from the transmitter to one or more otherrecipients than said receiver between packets of said packet stream;transmitting from the transmitter to the receiver an indication of saiddata transmitted to the one or more other recipients; receiving back anestimate of a bandwidth of said channel generated by the receiver usingsaid indication; and using the estimated bandwidth to controltransmission of packets from the transmitter.
 25. A computer programproduct for controlling transmission of packets from a transmitter to areceiver via a channel, the program product comprising code embodied ona computer-readable medium and configured so as when executed at atransmitter to: transmit a packet stream to the receiver; transmit datato one or more other recipients than said receiver between packets ofsaid packet stream; transmit to the receiver an indication of said datatransmitted to the one or more other recipients; receive back anestimate of a bandwidth of said channel generated by the receiver usingsaid indication; and use the estimated bandwidth to control transmissionof packets from the transmitter.
 26. A transmitter for controllingtransmission of packets from the transmitter to a receiver via achannel, the transmitter being configured to: transmit a packet streamto the receiver; transmit data to one or more other recipients than saidreceiver between packets of said packet stream; transmit to the receiveran indication of said data transmitted to the one or more otherrecipients; receive back an estimate of a bandwidth of said channelgenerated by the receiver using said indication; and use the estimatedbandwidth to control transmission of packets from the transmitter.
 27. Amethod for use in controlling transmission of packets from a transmitterto a receiver via a channel, the method comprising: receiving a packetstream at the receiver from the transmitter; at an estimation functionof the receiver, receiving from the transmitter an observation ofcross-traffic, the cross-traffic being an amount of data transmittedfrom the transmitter to one or more other recipients than said receiverbetween packets of said packet stream; and in the estimation function atthe receiver, using the observation of the cross-traffic to generate anestimate of a bandwidth of said channel; such that transmission ofpackets from the transmitter is controlled using the estimatedbandwidth.
 28. A computer program product comprising code embodied on acomputer-readable medium and configured so as when executed at areceiver to: receiving a packet stream from a transmitter via a channel;receive from the transmitter an observation of cross-traffic, thecross-traffic being an amount of data transmitted from the transmitterto one or more other recipients than said receiver between packets ofsaid packet stream; and use the observation of the cross-traffic togenerate an estimate of a bandwidth of said channel; such thattransmission of packets from the transmitter is controlled using theestimated bandwidth.
 29. A receiver arranged to receive a packet streamfrom a transmitter via a channel, the receiver comprising: an estimatorfunction arranged to receive from the transmitter an observation ofcross-traffic, the cross-traffic being an amount of data transmittedfrom the transmitter to one or more other recipients than said receiverbetween packets of said packet stream; and wherein the estimatorfunction is configured to use the observation of the cross-traffic togenerate an estimate of a bandwidth of said channel, such thattransmission of packets from the transmitter is controlled using theestimated bandwidth.